Hapln1a promotes atrial growth. (A–C) mRNA in situ hybridization analysis of hapln1a expression at 26hpf in embryos from an incross of hapln1aΔ241 heterozygous carriers. Wild-type and heterozygous siblings express hapln1a in the heart (bracket A, B, respectively), whereas hapln1a is absent in homozygous mutants (arrow C). (D–I) mRNA in situ hybridization expression analysis at 50hpf of myl7 (D–F) and myh6 (G–I) in wild-type siblings (D and G), hapln1aΔ241 heterozygous siblings (E and H) or hapln1aΔ241 homozygous mutant embryos (F and I). Scale bar = 50 μm. (J and K) Quantification of atrial area (J), and atrial outer curvature (K) in ISH-processed sibling embryos (wt/het) and hapln1aΔ241 or hapln1aΔ187 mutants (mut) at 50hpf. Atrial area is significantly reduced in hapln1aΔ241 mutants compared to wild-type siblings (P = 0.013), and atrial outer curvature is significantly reduced in both hapln1aΔ187 and hapln1aΔ241 mutants (P = 0.033 and P = 0.032). In both J and K, n = 54 hapln1aΔ187 wt; 104 hapln1aΔ187 het; 60 hapln1aΔ187 mut, 66 hapln1aΔ241 wt; 116 hapln1aΔ241 het; 53 hapln1aΔ241 mut. (L–O) Maximum intensity projections of light-sheet z-stacks of live 50hpf (L and M) and 72hpf (N and O) Tg(myl7:lifeActGFP); Tg(fli1a:AC-TagRFP) transgenic wild-type (L and N), and hapln1aΔ241 mutant embryos (M and O). Scale bar = 50μm. (P and Q) Quantification of atrial area (P), and atrial outer curvature (Q) in live light-sheet z-projections from wild-type sibling embryos and hapln1aΔ241 or hapln1aΔ187 mutants at 50hpf and 72hpf. Atrial area and atrial outer curvature are significantly reduced in hapln1aΔ241 mutants (mut) compared to wild-type siblings (wt/het) at 50hpf (P = 0.0002, and P = 0.014). In both (P) and (Q), n = 4 hapln1aΔ187 50hpf wt; 5 hapln1aΔ187 50hpf mut, 7 hapln1aΔ241 50hpf wt; 10 hapln1aΔ241 50hpf mut; 4 hapln1aΔ187 72hpf wt; 7 hapln1aΔ187 72hpf mut, 9 hapln1aΔ241 72hpf wt; 10 hapln1aΔ241 72hpf mut. Comparative statistics carried out using a Kruskal–Wallis test with multiple comparisons.
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